Polarization Maintaining Optical Delay Circuit

Abstract

The invention relates to a polarization maintaining optical delay circuit ( 1 ) for providing a time delay to an incident light (S 1 ), comprising an optical directional element ( 11 ) adapted for directing an incident light (S 1 ) from a first port ( 111 ) to a second port ( 112 ) and directing a returning light from the second port to a third port ( 113 ), a mirror element ( 12 ) adapted for reflecting the incident light (S 1 ), thereby changing the polarization state, so that the returning light (S 2 ) has a substantially orthogonal polarization state compared to the polarization state of the incident light (S 1 ), and an optical waveguide ( 13 ) adapted for optically connecting the second port ( 112 ) of the optical directional element ( 11 ) and the mirror element ( 12 ). The invention also relates to a ring cavity ( 2,3 ) comprising such an optical delay circuit, and an optical interferometer ( 4,5 ) with said optical delay circuit.

1 - 13 . (canceled) 
   
   
       14 . An optical delay circuit for providing a polarization maintaining delay to an incident light, comprising:
 an optical directional element adapted for directing an incident light from a first port to second port and directing a returning light from the second port to a third port,   a mirror element adapted for reflecting the incident light, thereby changing the polarization state, so that the returning light has a substantially orthogonal polarization state compared to the polarization state of the incident light, and   an optical waveguide adapted for optically connecting the second port of the optical directional element and the mirror element, the optical waveguide comprising a dispersion compensating device.   
   
   
       15 . The delay circuit of  claim 14  wherein the optical waveguide is designed to one of: being dispersion free, and compensating a dispersion of an optical circuit being connected to the delay line. 
   
   
       16 . The delay circuit of  claim 14 , wherein the optical waveguide comprises a section being a dispersion compensating fiber. 
   
   
       17 . The delay circuit of  claim 16 , wherein the optical waveguide comprises a single mode fiber section connected in series to the dispersion compensating fiber section. 
   
   
       18 . The delay circuit of  claim 14 , wherein the optical directional element comprises a polarization dependent beam splitter that is adapted to select the light fraction of a first main polarization axis of the incident light to be coupled from the first port to the second port, and the light fraction of the other main polarization axis of the returning light to be coupled from the second port to the third port. 
   
   
       19 . A ring cavity comprising:
 means for constituting an optical path for a circulating optical light,   a gain medium located within the optical path, and   the optical delay circuit of  claim 14 , wherein the optical delay circuit is connected in the optical path through the first port and the third port.   
   
   
       20 . The ring cavity of  claim 19 , further comprising an optical coupler connected into the optical path for coupling out a fraction of the circulating light as output light. 
   
   
       21 . The ring cavity of  claim 20 , further comprising an opto-electrical converter adapted for receiving the output light and generating an electrical signal oscillating at frequencies corresponding to differences of frequencies of different modes of the circulating light. 
   
   
       22 . The ring cavity of  claim 19 , further comprising an optical isolator connected into the optical path so that the circulating light circulates in one defined direction. 
   
   
       23 . The ring cavity of  claim 19 , wherein the optical path is realized by a polarization maintaining optical fiber. 
   
   
       24 . The ring cavity of  claim 19 , wherein the optical path is a free space circuit comprising a plurality of edge mirrors, wherein the gain medium is realized as semiconductor optical amplifier and the optical directional element is realized as polarization dependent beam splitter, and further comprising a half wave plate inserted into the optical path for adapting the polarization state of the returning beam to the polarization state of the incident beam. 
   
   
       25 . An optical interferometer comprising:
 an optical input for receiving an input optical signal,   splitting and combining means for splitting the input optical signal onto two optical paths and combining the signals split onto the two paths into an output optical signal,   wherein one of the optical paths comprises the optical delay circuit of claim  1 .   
   
   
       26 . The optical interferometer of  claim 25 , wherein both optical paths are each terminated by an optical mirror, wherein the splitting and combining means is realized as a four port optical coupler that is adapted to split the input optical signal received a first coupler port into two partial signals emitted a second and a third coupler port connected to each one of the two paths, to receive each a reflected signal reflected by the optical mirrors at the second and third coupler port, and to emit the output optical signal at a fourth coupler port. 
   
   
       27 . A method of providing a time delay to an incident light, comprising:
 directing an incident light from an input port to a first end of an optical waveguide,   generating at a second end of the optical waveguide a returning light by reflecting and changing the polarization state of the incident light, so that the returning light has a substantially orthogonal polarization state compared to the polarization state of the incident light, and   directing the returning light from the first end of the optical waveguide to an output port.